The invention relates to percussion fuses for munitions shells, and more particularly to percussion fuses assemblies interposed between a charge-containing shell body and a shell head disposed forwardly of the shell body.
In conventional percussion fuse assemblies of this type, a firing pin extends rearwardly from a rear surface of the shell head, and the percussion cap which is ignitably cooperable with the firing pin is carried in an impact member that is slidably disposed in a fixed sleeve portion of the fuse assembly. In order to normally maintain the impact member in its rear-most position to prevent engagement of the firing pin and the percussion cap, a selectively dischargeable blocking sphere is carried in mating apertures in the wall of the impact body and the surrounding fixed sleeve.
A second, inertia-influenced sphere is normally disposed in a front recess of the impact member during the acceleration portion of the shell flight, and is thereafter movable inertially forwardly of the recess and into a receiving recess situated in the shell head. When such inertial sphere is in its forward position, the impact member is free to be propelled forwardly upon impact of the shell with the target, thereby causing the percussion cap to impact the primer and be detonated thereby.
In one proposed arrangement of this type, the sphere-receiving groove in the shell head is radially offset from the recess in the impact member, so that if the shell encounters an obstacle, such as camoflage, during the acceleration portion of its flight, the sudden forward movement of the impact member, and thereby of the inertial sphere disposed in its recess, will cause such sphere to be wedged between the wall of the recess and the radial step at the rearward end of the sphere-receiving recess in the shell member. As a consequence, the impact member is prevented from moving to its front-most position, and thereby prevents the premature contact of the percussion cap with the firing pin.
While this fail-safe feature is generally desirable, it can inhibit somewhat the normal inertial forward travel of the sphere from the recess in the impact member to the recess in the shell head, particularly when the shell exhibits a relatively large degree of rotation about its longitudinal axis. In particular, during such rotational movement, a force component is generated that opposes the inertial forward movement of the sphere, so that such sphere may not have sufficient forward velocity to move into the radially offset recess in the shell head. Thus, when the impact member is shot forwardly during contact with the target, the failure of the sphere to reach the rear surface of the radially displaced recess in the shell head will cause such sphere to be wedged between such step and the wall of the recess in the impact member, exactly as if the shell had hit an obstacle during the acceleration phase of its flight.